Subcritical spoke for hub to rotor attachment

ABSTRACT

The present invention is a energy storage apparatus. The energy storage apparatus includes a rotor and a stator and a hub rotatably positioned about a stationary axial shaft. The hub also includes at least one spoke plane projecting radially from the hub, and the at least one spoke plane contains at least one spoke. The at least one spoke includes an in-plane bending stiffness exceeding an out-of-plane bending stiffness.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The present invention relates generally to hybrid vehicles, and, moreparticularly, to an energy storage apparatus for a hybrid motor vehicle.

2. Description Of The Related Art

Since the invention of powered vehicles, many different powertrainsystems have been attempted, including a steam engine with a boiler oran electric motor with a storage battery. It was, however, thefour-stroke internal combustion engine invented by Otto in 1876, and thediscovery of petroleum in 1859 that provided the impetus for the modernautomotive industry.

Although gasoline emerged as the fuel of choice for automotive vehicles,recent concerns regarding fuel availability and increasingly stringentFederal and State emission regulations have renewed interest inalternative fuel powered vehicles. For example, alternative fuelvehicles may be powered by methanol, ethanol, natural gas, electricityor a combination of fuels.

A dedicated electric powered vehicle offers several advantages:electricity is readily available; an electric power distribution systemis already in place; and an electric powered vehicle produces virtuallyzero emissions. There are several technological disadvantages that mustbe overcome before electric powered vehicles gain acceptance in themarketplace. For instance, the range of an electric powered vehicle islimited to approximately 100 miles, compared to about 300 miles for agasoline powered vehicle. Further, the top speed is about half that of asimilar gasoline powered vehicle. Significant advances in batterytechnology are required to overcome these technological disadvantages.

A hybrid powered vehicle, powered by electric and a gaseous fuel,overcomes the technical disadvantages of a dedicated electric vehiclewhile having almost the same environmental benefit as a dedicatedelectric vehicle. The performance and range characteristics arecomparable to a conventional gasoline powered vehicle.

Therefore, there is a need in the art for a hybrid powertrain system inan automotive vehicle that is energy efficient, has low emissions, andoffers the performance of a conventional gasoline powered vehicle.

SUMMARY OF THE INVENTION

It is, therefore, one object of the present invention to provide anenergy storage apparatus for a motor vehicle.

It is another object of the present invention to provide an energystorage apparatus for a hybrid powertrain system in a motor vehicle.

It is yet another object of the present invention to provide a flywheelenergy storage apparatus for a hybrid powertrain system in a motorvehicle.

It is still another object of the present invention to provide aflywheel energy storage apparatus to replace the battery in a hybridelectric motor vehicle.

It is still yet another object of the present invention to provide aflywheel energy storage apparatus that includes a hub with minimizedcentrifugal stress.

It is a further object of the present invention to provide a flywheelenergy storage apparatus that includes a hub having at least one spokeplane having at least one spoke.

It is still a further object of the present invention to provide aflywheel apparatus with a spoke having a sub-critical shape.

It is yet a further object of the present invention to provide aflywheel apparatus that includes a spoke shape that tapers nonlinearlyalong an increasing radius.

It is still yet a further object of the present invention to provide aflywheel apparatus with a hub and rotor attachment having a resonantfrequency exceeding the maximum operating speed of the rotor.

To achieve the foregoing objects, the present invention is a energystorage apparatus. The energy storage apparatus includes a rotor and astator and a hub rotatably positioned about a stationary axial shaft.The hub also includes at least one spoke plane projecting radially fromthe hub, and at least one spoke plane contains at least one spoke. Theat least one spoke includes an in-plane bending stiffness exceeding anout-of-plane bending stiffness.

One advantage of the present invention is that a new and improved energystorage apparatus for a motor vehicle is provided. Another advantage ofthe present invention is that an energy storage apparatus such as aflywheel is provided for a hybrid powertrain system in a motor vehicle.Yet another advantage of the present invention is that the flywheelreplaces the battery in a hybrid electric motor vehicle. Still yetanother advantage of the present invention is that a energy storageapparatus is provided that includes a hub with minimized centrifugalstress. A further advantage of the present invention is that a energystorage apparatus is provided with a hub having at least one spokeplane, and the at least one spoke plane has at least one spoke. Yet afurther advantage of the present invention is that the spoke has a subcritical shape with higher in-plane bending stiffness allowing forhigher operating speeds of the rotor without having to pass through acritical speed. Yet still a further advantage of the present inventionis that the shape of the spoke tapers nonlinearly along an increasingradius to minimize centrifugal stress. Yet another advantage of thepresent invention is that the resonant frequency of the hub and therotor exceed the maximum operating speed of the rotor.

Other objects, features and advantages of the present invention will bereadily appreciated as the same becomes better understood after readingthe subsequent description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a hybrid powertrain system for anautomotive vehicle according to the present invention.

FIG. 2 is a block diagram of an operational relationship of a hybridpowertrain system for an automotive vehicle according to the presentinvention.

FIG. 3 is an elevational view of an energy storage apparatus accordingto the present invention.

FIG. 4 is a isometric view of the exterior of an energy storageapparatus according to the present invention.

FIG. 5 is a cut-away view of an energy storage apparatus according tothe present invention.

FIG. 6 is a cut-away view of a rotor according to the present invention.

FIG. 7 is a side view of the rotor and hub interface according to thepresent invention.

FIG. 8 is a sectional view taken along lines 8--8 of FIG. 7 of the rotorand hub interface according to the present invention.

FIG. 9 is a perspective view of an optical encoder disc according to thepresent invention.

FIG. 10A is a sectional view taken along lines 10--10 of FIG. 9 of anoptical encoder disc according to the present invention.

FIG. 10B is an enlarged view of circle 9 of FIG. 9 of the slots in anoptical encoder disc according to the present invention.

FIG. 11 is a flowchart of a methodology for assembling a winding to astator according to the present invention.

FIGS. 12A through 12M are an illustrative flowchart of a method forconstructing the rotor according to the present invention.

FIG. 13 is a flowchart of a methodology for assembling a magnet to a rimaccording to the present invention.

FIG. 14 is a perspective view of an alternative rim construction for therotor according to the present invention.

FIG. 15 is a plan view of a gimbal support system according to thepresent invention.

FIG. 16 is a side view of a gimbal support system according to thepresent invention.

FIG. 17 is a side view of a stator according to the present invention.

FIG. 18 is a plan view of a winding forming fixture according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIG. 1, a hybrid powertrain system is illustrated for avehicle. The vehicle 100 is partially shown in a cut away viewillustrating a hybrid powertrain system 105 disposed within a chassis110. The hybrid powertrain system 105 includes a gas powered turbineengine 115, which in this example is fueled by liquefied natural gas.The turbine engine 115 spins an alternator 120 to generate electricpower to operate the vehicle. It should be appreciated that in thisexample there are two alternators 120 that run at different speeds, suchas 60,000 rpm and 100,000 rpm, to produce electricity equivalent to 500horsepower. It should also be appreciated that the engine 115 andalternator 120 are known as a turboalternator.

A power or vehicle management controller 135 such as a power controlleris in communication with the turbine 115 and alternator 120, and managesthe distribution of power within the hybrid powertrain system 105. Thepower controller directs the transfer of power from the alternator 120to a traction or induction motor 125 using a power transfer mechanism140, such as a three phase Variable Frequency Alternating Current(VFAC). In this example the traction motor 125 is an AC induction motor125 capable of producing greater than 750 horsepower. The motor 125 thentransfers the power to the drivetrain 145 and eventually the wheels 150to operate the vehicle 100.

The power controller 135 is also in communication with an energy storageapparatus 130 such as a flywheel. It should be appreciated that theflywheel 130 replaces a battery (not shown but well known in the art) asa conventional vehicle power source. The power controller 135 directsthe power from the alternator 120 through VFAC lines 140 to the flywheel130 for storage during periods of low power demand. The power controller135 also directs the stored power from the flywheel 130 to the motor 125during periods of high power demand.

Preferably, the hybrid powertrain system 105 also includes varioussensors which are conventional and well known in the art. The outputs ofthese sensors communicate with the power controller 135. It should alsobe appreciated that the vehicle 100 includes other hardware not shown,but conventional in the art to cooperate with the hybrid powertrainsystem 105.

Referring to FIG. 2, the operational relationship of a hybrid powertrainsystem for an automotive vehicle is illustrated. An input from anoperator such as a driver is communicated to the power controller 135.If the driver input requires increased power, the power controller 135directs the turbine 115 and alternator 120 and if necessary the flywheel130, to supply power to the motor 125, which in turn supplies power tothe drivetrain 145 and eventually to the wheels 150. Alternately, if thedriver input indicates decreased power needs, the power controller 135directs the excess power capacity from the turbine 115 and alternator120 into the flywheel 130 for storage.

Referring to FIGS. 3 through 6 an energy storage apparatus isillustrated. The energy storage apparatus 500 according to thisinvention is a flywheel 505, such as that used in a hybrid powertrainsystem 105 in an automotive vehicle 100. The flywheel 505 has a rotor510 and stator 515 disposed within a vacuum container such as a housing520. The rotor 510 rotates about the stator 515. The flywheel 505 storeskinetic energy by rotating at increasingly higher speeds. Similarly, theflywheel 505 releases its stored kinetic energy by slowing its rotation.The rotating components within the flywheel 505 are subjected to highcentrifugal loading, causing them to grow radially outward. It should beappreciated that in this example the flywheel 505 weighs approximately120 pounds and spins at speeds of up to 53,000 rpm.

The stator 515, having a generally cylindrical shape, is fixedlydisposed within the housing 520. It should be appreciated that in thisexample the stator 515 is attached at a first end (not shown) to thehousing 520, and at a second end to a stationary axial shaft 585 by asuitable means.

Referring also to FIG. 17, a stator 515 is illustrated. The stator 515includes a bobbin 522 having a sleeve-like shape. Preferably, the bobbin522 is constructed from a non-magnetic, thermally conductive,electrically non-conductive material with low permeability, such as aceramic so that the bobbin 522 is electrically and magneticallytransparent. Therefore, as the electric fields move around, the flow ofthe magnetic field is not impeded. The bobbin 522 includes at least onecooling passage 523 for the transportation of a cooling medium, such aswater. The bobbin 522 also includes at least one cooling slot 524.Positioned adjacent the at least one cooling passage 523 is at leastone, and preferably a plurality of longitudinally extending fins 525 onthe exterior surface of the stator 515. The fin 525, as well as thecooling passage 523 dissipates the rising heat in a winding 530. Thephase winding 530 axially encircles the bobbin 522, and is separated bythe fin 525. The winding 530 is made from a suitably conductivematerial, such as copper in this example. The passing of alternatingcurrent through the winding 530 creates a magnetic field in an air gap562 between the rotor 510 and stator 515 (to be described).

Preferably, the winding 530 is preformed prior to installation on thebobbin 522. A forming fixture 540 resembling a long plate having "S"shaped grooves 541 therein is used to preform the winding 530 asillustrated in FIG. 18. The winding 530 is placed within the grooves 541of the forming fixture 540.

The winding 530 includes an upper end turn 542 located at an upper endof the bobbin 522, and a lower end turn 545 located at a lower end ofthe bobbin 522. The winding 530 and each end turn 542, 545 respectivelyform a closed circuit for the winding 530. A wiring assembly 555 (shownin phantom) is connected at one end to the upper end turn 542 and at theother end to the power controller 135.

Referring back to FIGS. 3 through 6, rotor 510, having a generallycylindrical shape in this example, is rotatably supported within thehousing 520. The rotor 510 includes a rim 556, with a magnet 560 and amass 565 disposed on a surface of the rim 556. It should be appreciatedthat in this example the rotor 510 is positioned such that itcircumscribes the stator 515. It should also be appreciated that in thisexample the cylindrical length of the rotor 510 is greater than that ofthe stator 515. The magnet 560 interacts with the magnetic field createdby the electrical currents passing through the winding 530 and creates aforce which creates a motion, rendering the rotation of the rotor 510.

The magnet 560 is also a source of induced voltage generated in thewindings 530 in the stator 515. The output voltage generated by themagnet 560 is a function of a gap 562 between the stator winding 530 andrim 556, and the speed of the rotor 510, providing other factors areconstant. The flywheel 505 uses centrifugal force growth as the rotors510 speed increases to regulate the output voltage. Therefore, thevoltage range is reduced and current requirements are reduced. Theflywheel 505 is lighter, smaller and more efficient because the currentrequirement is reduced.

Preferably, the rim 556 is fabricated from a high strength compositematerial such as a carbon/fiber composite. In this example, the rim 556includes a plurality of rim segments or disks 810, as shown in FIG. 12A,balanced and bonded together using a high strength epoxy such asHercules 8552. Each segment 810 is oriented radially to the others todistribute the imbalance of each segment 810 to achieve an optimum rim556 balance, while minimizing the bonding stress between adjacentsegments 810. The interior surface of the rim 556 is divided into afirst rim section 557 which is adjacent to the stator 515, and a secondrim section 558 which is not adjacent to the stator 515. The firstsection 557 includes a magnet 560 disposed thereon. It should beappreciated in the example the magnet 560 is composed of a plurality ofmagnet segments. Preferably, the magnet 560 is a segmented rubberizedsoft magnet to survive in the environment of a growing flywheel 505.Typically, rare earth magnets are very brittle, and since the flywheel505 grows approximately 2%, a rare earth magnet would not survive.Therefore, a soft magnet 560 includes pulverizing a magnet 560 intomicroscopic particles and adding rubber to the particles. An oxidecoating is then applied to the magnet 560.

The second section 558 includes a mass 565, such as a balance weight,disposed thereon. It should be appreciated that in this example the mass565 simulates the weight of the magnet 560 to ensure uniform radialgrowth of the rotor 510 as it rotates. Further, the uniform bore loadingminimizes rotor 510 shear stresses as well as radial stresses.

A hub 580 rotatably interfaces with an axially positioned stationaryshaft 585. In this example the hub 580 interfaces with the shaft througha plurality of mechanical bearings (not shown but well known in the art)At least one, and preferably a plurality of spoke planes 582 having atleast one radially extending spoke 584, preferably a plurality, radiatein an outwardly manner from the hub 580. The end of the spoke 584slidingly engages the rotor 510. The sliding spoke interface allows forhub 580 growth and relative movement between the spokes 582 and the rim510 under high centrifugal force as the rotor speed increases. In thisexample there are two spoke planes 582 each having eight spokes 584. Thespokes 584 are, for example, at 45 and 90 degrees from each otherrespectively to maintain hub 580 and rotor 510 balance while allowingfor growth. The hub 580 and spokes 584 in this example are fabricatedfrom a high strength steel such as AERMET 100.

The critical speed is the rotational speed where the spoke 584 exhibitsbending. A thinner more flexible or super critical spoke 584 has a lowercritical speed, whereas a stiffer, thicker spoke 584 has a highercritical speed. If the spoke 584 has a thicker shape with a higher inplane bending stiffness, the rotating spoke 584 is sub-critical becauseit moves the resonant frequency of the hub and rotor above the maximumoperating speed of the flywheel 580. Therefore, a subcritical spoke 584allows for higher operating speeds without having to pass through acritical speed as in a supercritical spoke design 584. In this examplethe shape of the spoke 584 tapers from thicker adjacent to the hub 580,to thinner near the rim 510. It should be appreciated that the optimumshape of the spoke 584 is preferably a non-linear taper to minimizecentrifugal stresses, while maintaining adequate stiffness.

Referring also to FIGS. 7 and 8, the rotor to hub interface 590 isillustrated. A socket 592 is disposed between the spoke 584 and therotor 510. Preferably, aluminum is used for the socket 592 because it islight-weight, yet relatively strong. In this example the socket 592 isshaped to slidingly engage an end of a spoke 584. A middle layer 594having an adhesive on each side is interposed between the socket 592 andthe rotor 510 to distribute loads exerted on the rotor. Preferably, themiddle layer 594 is formed from a material which allows hoop strainmismatch between the composite rotor 510 and the socket 592, such aspolyethylene.

In the preferred embodiment, an attachment receptacle 570 includes apair of sockets 592 on either end of a solid bar 595 to simultaneouslyengage with a spoke 584 from each of the two spoke planes 582. In thisexample, there are eight attachment receptacles 570 in each spoke plane582, and the attachment receptacles 570 are bonded to the rotor 510, aspreviously described.

A plurality of longitudinally extending balance bars 596 are positionedbetween each attachment receptacle 570. The balance bars 596 aredesigned to match the centrifugal loading imparted on the rotor 510 bythe adjacent receptacle 570, and magnet 560, improving the stressefficiency of the rim 556. Preferably, the balance bar 596 is fabricatedusing a laminate construction technique to minimize eddy currents. Inthis example, there are 6 balance bars 596 adjacent a spoke 584. Thebalance bars 596 are bonded to the rotor 510. To balance the rotor 510,material may be removed from the balance bar 596. Preferably, the middlelayer 594 having an adhesive on each side is interposed between thebalance bar 596 and the rotor 510.

A speed and position sensing mechanism provides the power controller 135described in FIG. 2 with information regarding how fast the hub 580 isrotating or the relative position of the hub 580. For example, anoptical encoder disc 600 disposed on the hub 580 passes through astationary read head mechanism 605 as the hub 580 rotates. In thisexample the read head 605 is positioned on the stator 515. The read headmechanism 605 transmits the speed and position of the hub 580 to thepower controller 135, to control the energy storage capability of theflywheel 505.

Referring to FIG. 9, 10A and 10B, an optical encoder disc 600 isillustrated. The encoder disc 600 has a generally circular shape, andthe center of the disc 610 has an opening therein for centering theencoder disc on the hub 580. The disc 610 is attached to the hub 580 bya suitable means, such as with bolts 615. The disc 600 rotates with thehub 580 at a high speed and is subject to centrifugal loading.Therefore, construction considerations of the disc 600 include that itremain flat, relatively axially rigid, and has acceptable radial growthas it rotates.

A first radial length of the encoder disc 600 includes at least one,preferably a plurality of slots 620 equally spaced around the perimeterof the disc 600. For example, the length of a slot 620 is approximately0.015 in., width 0.006 in., and there are 10 slots 620 in number. Asecond radial length includes at least one, preferably a plurality ofelongated slots 630 spaced around the perimeter of the disc 600. Forexample, there are 1280 elongated slots 630 in number.

The disc 600 is thickest at its rotational axis, and is progressivelythinner toward the outer edge of the disc 600 until the maximum lightpasses through the slots 620, 630 with minimum reflection and fringeeffects. If the disc 600 had a uniform thickness throughout, then as thedisc 600 was rotating, the resulting radial growth would affect theaccuracy. By progressively decreasing the thickness of the disc along anincreasing radius 625, the original geometry and alignment of the disc600 with the read head 605 is maintained.

Referring to FIG. 11, a methodology for assembling the winding 530 tothe stator 515 is illustrated. The winding 530 is preshaped on a formingfixture (not shown but well known in the art) and then installed on thebobbin 522. The forming fixture defines the outer diameter of thefinished stator 515 and draws a potting medium such as an epoxy into thedesired locations. The methodology begins in block 532 by dividing acylindrical forming fixture into a plurality of segments, such as four.The fixture includes a slightly compressible seal made from a materialsuch a aluminum at each of the joints separating a segment. The sealprevents the entry of epoxy during potting. Advancing to block 534, themethodology positions the fixture around the fins 525, shaping thewindings 530 into a cylindrical form. Advancing to block 536, themethodology compresses the seal forming a seal. Advancing to block 538,the methodology pots the winding 530, as is known in the art, such asunder alternate cycles of vacuum and pressure.

Referring to FIGS. 12A through 12M, a methodology for constructing arotor 800 is illustrated. The rim 805 is exposed to hoop stress, orinternal loads in a circumferential direction. Therefore, hoop stressefficiency to minimize stress is accomplished by the constructionmethodology of this example. Radial, axial and shear stresses are alsoconsidered.

The methodology begins in Step 1 and at least one, preferably aplurality of rim segments 810 or disks are fabricated, such as bywrapping a hoop with tape. Proceeding to Step 2 as shown in FIG. 12A,the rim segments 810 are bonded together. In this example, each rimsegment is balanced and bonded to another rim segment 810 using a highstrength epoxy such as Hercules 8552 resin. Each segment 810 is orientedradially to the others to distribute the imbalance of each segment 810to achieve an optimum rim 805 balance, while minimizing the bondingstress between adjacent segments 810. Proceeding to Step 3, a firstlamina panel 815 is fabricated, such as a 1 ply panel of +/-45° epoxygraphite. In this example, lamina panels of + and -45° are usedthroughout, because as the rim 805 grows, the wrap will pull the rim 805together, reducing its axial shear stress. Proceeding to Step 4 as shownin FIG. 12B, the lamina panel 815 is bonded to the inner diameter of therim 825. It should be appreciated that in this example the lamina panel815 is applied in two pieces.

Proceeding to Step 5, a second lamina panel is fabricated 820, such as a2-ply panel of +/-45° epoxy graphite. Proceeding to Step 6 as shown inFIG. 12C, the second lamina panel 820 is bonded to the inner diameter ofthe rim 825. It should be appreciated that in this example the laminapanel 820 is applied in two pieces, such that the seam lines of thefirst and second lamina panels 815, 820 are staggered.

Proceeding to Step 7, a third lamina panel 825 is fabricated, such as a2-ply panel of +/-45° epoxy graphite. Proceeding to Step 8 as shown inFIG. 12D, the third lamina panel 830 is bonded to the outer diameter ofthe rim 835. It should be appreciated that in this example the laminapanel 830 is applied in four pieces. Proceeding to Step 9 as shown inFIG. 12E, the outer diameter of rim 835 and inner diameter of rim 825and top and bottom radii are machined to have a radius end. The roundedshape of the top and bottom radii will reduce high stress corners.

Proceeding to Step 10 as shown in FIG. 12F, the mass 565 and magnet 560are prepared. Preferably, the mass 565 is constructed of segments havinglaminated layers; including two end mass segments 840 of tantalumlaminate bonded together with UHMW polyethylene, and a middle masssegment 845 of G-10 laminate bonded together with UHMW polyethylene. Itshould be appreciated that end mass segments 840 are placed on the innerdiameter to help contain the magnets 560 and balance the mass 845axially. Preferably, Tantulum is used for the end mass segments 840because its high density and laminated construction allow the segmentdensity to be tuned to match that of the magnet 560, thereforegenerating equivalent centrifugal forces along the radius. Tantulum isalso advantageous because it is soft radially, stiff axially and offersno magnetic resistance. The shape of the Tantulum end mass segment 840is chosen to minimize intra-lamina shear stress of the rim 556. TheTantulum lamina are bonded together with polyethylene. The laminatedconstruction eliminates eddy currents. It should also be appreciatedthat G-10, in combination with the receptacle 570 and balance bar 596,provide centrifugal loading to the rim 556 equal to that of the magnet560 alone.

Proceeding to Step 11 as shown in FIG. 12G, the magnet 560 is bonded tothe inner diameter of the rim 825. Preferably the magnet 560 is aplurality of magnet segments. Proceeding to Step 12 as shown in FIG.12H, the mass segments 840, 845 are bonded to the rim 825.

Proceeding to Step 13, a fourth lamina panel 855 is fabricated, such asa 2-ply panel of +/-45° epoxy glass. Proceeding to Step 14 as shown inFIG. 12I, the fourth lamina panel 855 is bonded to the inner diameter ofthe rim 825. It should be appreciated that in this example the laminapanel 855 is applied in 4 pieces. Proceeding to Step 15 as shown in FIG.12J, a plurality of inner ply segments 860 are prepared, such are from+/-45° epoxy glass. Proceeding to Step 16 as shown in FIG. 12K, theinner segments 860 are arranged two layers thick on the inner diameterof the rim 825 and onto the top and bottom radii, and bagged and curedas is known in the art.

Proceeding to Step 17 as shown in FIG. 12L, a plurality of outer plysegments 865 are prepared, such are from +/-45° epoxy graphite.Proceeding to Step 18 as shown in FIG. 12M, the outer segments 865 arearranged two layers thick on the outer diameter of the rim 835, onto thetop and bottom radii and into the inner diameter of the rim 825, andbagged and cured as is known in the art. It should be appreciated thatthe carbon fiber or epoxy glass overwrap completely encloses the rim andis in tension to help contain the axial stress.

Referring to FIG. 13, a methodology for assembling the magnet to the rimis illustrated. The assembly of the magnet 560 to the first rim section511 is critical in controlling the gap 562 between the stator winding530 and the inner diameter of the magnet 560. The performance andefficiency of the flywheel 505 is affected by the dimension of the gap562. The methodology begins in block 965 by mounting a plurality ofmagnets 564 on a mandrel (not shown but well known in the art). Themethodology advances to block 970 and the outer diameter of the magnet560 is turned, as is known in the art, to a desired size. Advancing toblock 975, the methodology turns the inner diameter of the first rimsection 511 to a desired size. Advancing to block 980, the methodologyapplies adhesive to the outer diameter of the magnet and the innerdiameter of the first rim section 511. Advancing to block 985, themethodology slides the magnet into the rim section 511. Advancing toblock 990, the methodology heats the combined magnet and rim until theadhesive cures. Advancing to block 995, the methodology removes themandrel.

Referring to FIG. 14, an alternate construction of a rim for the rotoris illustrated. The alternate rim embodiment 900 includes a one piecerim 910 having filaments wound thereon and no outer overwrap. In a onepiece rim 910, the filaments would be predominantly wound in the 0°direction with a small proportion wound at a suitable bias angle toprovide the desired strength characteristics. It should be appreciatedthat 0° is pure hoop direction. A first section of the inner diameter ofthe rim 915 has at least one, preferably a plurality of magnets 920bonded thereon. A second section of the inner diameter of the rim 925has a mass 930 bonded thereon to simulate the weight of the magnet 920.A liner 935 is positioned adjacent the magnet 920 and mass 930 to alignthe magnet 920 and mass 930. Preferably, the liner 935 is constructedfrom one piece and has filaments wound around it. A cap 940 may bepositioned over an open end of the magnet 920 and an open end of themass 930 to prevent axial growth at the ends.

Referring to FIGS. 5, 15, and 16, a gimbal support system isillustrated. It should be appreciated that the gimbal system supports anapparatus mounted to a frame. The gimbal system 700 of this examplesupports the flywheel 505 from the chassis 110 of the vehicle 100,allowing the flywheel 505 to have uni-directional pitch and rollstiffness isolating it from the motion of the vehicle 100. For example,if the vehicle 100 turns a corner and the chassis 110 rolls, theflywheel 505 remains relatively stationary.

The gimbal system 700 includes at least two parallel flexible beams 705,such as a leaf spring in a Hotchkiss-type vehicle application. The beams705 are positioned on either side of the housing 520, extendingperpendicular to the spin axis of the flywheel 505. It should beappreciated that the total active length of each beam 705 is equal tothe distance between the beam 705 centers.

The flywheel 505 is centered between the beams 705, and attached by asuitable means, such as with bolts. A first and second end of each beam705 attaches to the chassis 110 of the vehicle 100. For example, a pairof opposing ledges 710 integral with the chassis 110 have a raised knifeedge for supporting the first and second end of the beam 705,respectfully. This type of support is advantageous due to its simplicityand light weight.

At least one dampening mechanism 725, such as an external damper,dampens the motion of the flywheel 505 relative to the motion of thevehicle 100. A first end of the dampening mechanism 725 attaches to thechassis 110 (not shown) and a second end of the dampening mechanism 725attaches to an external face of the flywheel housing 520, preferablynear the top centerline of the housing 520. Preferably, there are twodampers 725 each located 45 degrees from a centerline of the beam 705and 90° from a spin axis passing through the flywheel 505.

The present invention has been described in an illustrative manner. Itis understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.

Many modifications and variations of the present invention are possiblein light of the above teachings. Therefore, within the scope of theappended claims, the present invention may be practiced other than asspecifically described.

What is claimed:
 1. An energy storage apparatus having a rotor and astator comprising:a hub rotatably positioned about a stationary axialshaft; at least one spoke plane projecting radially from the hub,wherein said at least one spoke plane contains at least one spoke; andsaid at least one spoke having an in-plane bending stiffness exceedingan out-of-plane bending stiffness.
 2. The energy storage apparatus ofclaim 1, wherein:the resonant frequency of the hub and the rotor exceedsthe maximum operating speed of the flywheel.
 3. The energy storageapparatus of claim 1, wherein:said at least one spoke is of a decreasingthickness ex tending radially outward.
 4. An energy storage apparatushaving a rotor and a stator comprising:a hub rotatably positioned abouta stationary axial shaft; at least one spoke plane projecting radiallyfrom the hub, wherein said at least one spoke plane contains a pluralityof spokes; said spokes have a decreasing thickness extending radiallyoutward; and said spokes have an in-plane bending stiffness exceeding anout-of-plane bending stiffness.
 5. The energy storage apparatus of claim1, wherein:the resonant frequency of the hub and the rotor exceeds themaximum operating speed of the flywheel.